Method of packaging



METHOD OF PACKAGHNG William Ernest Henderson, Lockport, EL, assignor, by Inesne assignments, to Union Carbide Corporation, New York, N.Y., a corporation of New York No Drawing. Application February 4, 1955 Serial No. 486,264

6 Claims. (Cl. 53-30) This invention relates to packaging. More particularly it relates to a method of producing skin tight coverings on items packaged therein.

Various thermoplastic films are used extensively for wrapping and packaging. In the protective packaging of foods particularly poultry, meats, and meat food products for frozen storage or storage under refrigerating conditions the covering must be skin tight so that there will be substantially no pockets of entrapped air between the covering and the surface of the packaged item.

Bags made of films of unvulcanized rubber and certain types of Saran provide tight coverings on items inserted therein. In use the item was inserted in the bag and after the open end had been scaled the package was subjected to a temperature of 100 C. or lower as by immersion in boiling water for a short interval of time.

The aforementioned materials become brittle at the temperatures required for storage under refrigerating conditions or frozen storage and frequently split with the consequence that the desired results were not obtained during the life of the package.

Polyethylene film because of its chemical and physical properties is extensively used for wrapping and packaging. Because of its excellent low temperature durability it is admirably suited as a protective packaging material for foods such as poultry, meat, and meat food products for frozen storage or storage under refrigerating condition. However, in general, polyethylene film exhibits little or no shrinkage when subjected suddenly to boiling water. Recently there has been produced a polyethylene film which does shrink when suddenly subjected to heat at 100 C. but for some applications a greater shrinkage is desired.

An object of this invention is to provide a new and novel method of shrinking polyethylene film.

Another object of this invention is to utilize the aforementioned method in producing protective skin tight coverings.

Other and additional objects will become apparent hereinafter.

The invention is based on the surprising discovery that polyethylene film which does not shrink when suddenly subjected to a temperature of not over 100 C. will shrink when suddenly subjected to a temperature of over 100 C. and also that polyethylene film which shrinks when suddenly subjected to a temperature of not over 100 C. will shrink to a greater extent when suddenly subjected to a temperature of over 100 C. In both cases, very little, if any, wrinkling of the film is obtained.

The objects of the inventions are accomplished in general by inserting the item to be packaged in a polyethylene bag and after closing the open end suddenly subjecting the package to a temperature above 100 C. but below the melting point of the polyethylene, whereupon the bag will shrink and intimately conform to the surface of the item. In the preferred embodiment before the open end of the bag is closed the interior of the bag Patented June 16, 1959 is evacuated. The period of time during which the bag is subjected to the shrinking temperature is relatively small. In general, the heat can be applied for a period of 5 to 10 seconds. However, satisfactory results have been obtained by applying the heat for 2 to 3 seconds. The temperature to which the bag is subjected for obtaining shrinkage is above C. and below the melting point of the polyethylene. The preferred temperature is approximately eight degrees (0.) below that at which the film will lose its birefringence when observed between crossed Nichol prisms on a hot stage microscope and can. be determined empirically whenever desirable or necessary.

Any appropriate means or method for providing the desired temperature at which the shrinkage of the bag is to be efiected can be used. The desired temperature can be obtained through the use of heated air, steam, convection heating, etc. In the preferred embodiment the shrinkage is obtained by suddenly submerging the film in a liquid medium at the desired temperature. Any liquid medium which does not deleteriously affect the film constituting the bag and can be heated and maintained at the desired shrinking temperature can be used. The liquid medium can be a heat liquified solid, a pure liquid, or a solution which can be maintained at the desired shrinking temperature. In general, an aqueous solution having a boiling point at or above the temperature at which the shrinking is to be effected is preferred. When the contents of the package is a foodstuif, the liquid medium should also be non-toxic. Hereafter are illustrative liquid media and the temperatures at which they were employed for shrinking polyethylene film in accordance with this invention:

Liquid Medium: Temp. C.

Saturated aqueous NaCl soln. (B.P.) 108 Saturated aqueous NaCl soln. 95% corn syrup, 5% water (B.P.) 104 80% glycerin, 20% Water 105 60% glycerin, 40% water 105 Sat. aqueous sodium acetate soln. 105 Tetraethylene glycol 105 In order to more clearly show the results obtained by this invention, there is hereafter set out the percentage shrinkage of various polyethylene films when subjected to the temperatures set out.

Percent Shrinkage at- Polyethylene Thickness Film (M) 99-100 C. 105 C. 108 C.

MD TD MD TD MD RD A 2.0 41 18 50 30 54 31 B 2. 0 35 28 44 33 46 34 2. 0 35 25 46 32 45 31 1. 9 0 3 25 22 50 53 2. 0 0 0 l] 8 58 50 2.0 50 10 50 60 1.8 0 3 50 50 2. 2 28 29 48 43 2. 2 21 27 37 39 MD means machine direction. TD means transverse direction. No measurement.

The following method is used to determine shrinkage: A sample of film is cut to a size of 4 /2 inches by /2 inch, with the greater dimension being parallel to the direction of extrusion. A weight of 0.5-1.0 grams is clipped to one end of the sample, and the sample is marked at a position 4 inches from the free end. The sample is then held briefly by the free end, so that the weighted lower end is about 6 inches above the surface of a well-stirred liquid bath at the temperature in question, and allowed to fall freely. A screen about 6 inches below the surface of the hot liquid provides a convenient method of recovering the sample, which should remain submerged for ,seconds. The percentage of shrink in the machine direction is then determined by measuring the distance between the mark and the free end of the sample.

The test is repeated with a similar sample cut parallel to the transverse direction, in order to determinetra'ns verse shrinkage. Expansion is considered to be negative shrinkage for numerical convenience.

The shrinkable bag contemplated by this invention can be made by appropriately sealing one open end of seamless or seamed thin walled tubing with or without gussets as desired. Polyethylene tubing having a wall thickness within the range of .0005 to .0040 inch or more and preferably. within the range of 0.0018 to 0.0022 inch has been used. In the preferred embodiment bags made of seamless polyethylenetubing produced by" the method disclosed in my copending applicationlSerial No. 486,263 filed February 4, 1955 are used. i

The dimensions of the bags are such as will permit quick and ready insertion of the item tobe packaged therein and upon shrinking will intimatelyconform'to the item and form a protective skin tight covering very little if any wrinkling.

The invention is admirably suited for the packaging of eviscerated poultry such as turkeys, chickens, ducks, geese, pheasant, etc. for frozen storage as well asmeat food items such as whole meat loaves, smoked butts, whole pieces of sausage, whole cooked hams, smoked picnics (shoulder hams), bone-in and boneless smoked hams, sliced luncheon meats, sliced ham, sliced bacon, sliced sausage, whole slices or wedges of cheese, whole meat carcasses, fresh meat cuts such as chops, steaks, etc. for storage under refrigerating conditions. i

In carrying out the method the selected item is inserted in a polyethylene bag of appropriate size and the interior of the package is evacuated in any appropriate manner. The open end is then sealed and the package subjected suddenly to heat at a temperature of over 100 C. for a relatively short interval of time such as for example by suddenly submerging in a liquid medium at a temperature of 102-l08 C. or more for 2 to 3 seconds whereupon the bag will shrink and intimately conform to the surface of the item and form a protective coveringsubstantially free of wrinkles. When the item is for frozen storage the package including the shrunken bag is exposed to an operation wherein the item is quick frozen and thereafter stored under conditions to maintain a the item in the frozen state. If the item is one which is to be stored under refrigerating conditions, the package after shrinking of the bag is placed in a cooler at the appropriate temperature. In the event that the solution is one from which substances will precipitate or crystallize Saran, polymer modified vinyl copolymers, polymer or liquid plasticized polyvinyl chloride, polyethylene terephthalate (Mylar), etc. which exhibits little or no shrinkage upon sudden exposure to temperatures at or below C. or to obtain a greater shrinkage than obtained upon sudden exposure to temperatures at or below 100 C. In general the thickness of these films may be within the range of 0.0005 inch to 0.0040 inch or more.

Since it is obvious that various changes and modifications can be made in the above description Without departing from the nature and spirit thereof, this invention is not restricted thereto except as set forth in the appended claims.

I claim:

1. In a method of providing a protective skin tight covering the steps which comprise inserting the item to be packaged in a bag formed of polyethylene film and suddenly subjecting the package to a temperature of more than 100 C. and less than the melting point of the polyethylene constituting the film for a short interval of time.

2. In a method as set forth in claim 1 wherein the temperature to which the package is subjected is approximately eight degrees lower than that at which the film will lose its birefringence when observed under crossed Nichol prisms on a hot stage microscope.

3. In a method as set forth in claim 1 wherein the package is suddenly submerged in a liquid medium at a temperature above 100 C. and below the softening point of the resin.

4. In a method as set forth in claim 1 wherein the package is suddenly submerged in a liquid. at a temperature which is approximately 8 degrees (C.) lower than that at which it will lose its birefringence when observed under crossed Nichol prisms on a hot stage microscope.

5. In a method as set forth in claim 1 wherein the package is submerged suddenly in a saturated aqueous sodium chloride solution at a temperature of to 108 C.

6. In a method as set forth in claim 1 wherein the package is submerged suddenly in an aqueous glycerine solution containing 60% to 80% glycerine and correspondingly 40% to 20% water, the proportions being by volume.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Modern. Packaging, September 1950, pages 93, 94, 199, 200.

Dedication 2,890,552.W2'Zlimn Ernest Henderson, Lockport, I11. METHOD OF PACK- AGING. Patent dated June 16, 1959. Dedication filed May 24:, 1971, by the assignee, U m'on Carbide Corporation. Hereby dedicates to the People of the U.S. the remaining term of said patent.

[Ofim'al Gazette June 13, 1.972.] 

1. IN A METHOD OF PROVIDINGA PROTECTIVE SKIN TIGHT COVERING THE STEPS WHICH COMPRISE INSERTING THE ITEM TO BE PACKAGED IN A BAG FORMED FO POLYETHYLENE FILM AND SUDDENLY SUBJECTING THE PACKAGE TO A TEMPERATURE OF MORE THAN 100*C. AND LESS THAN THE MELING POINT OF THE POLYETHYLENE CONSTITUTING THE FILM FOR A SHORT INTERVAL OF TIME. 